Hydraulic apparatus



Nov. 9,1943. F. w. MEREDITH HYDRAULIC APPARATUS Filed Oct. 19, 1942 @w Nwmmw mmNm @hm ww.. uw ww mw Nw .mw Vx V N.

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Patented Nov. 9, 1943 UNITED f HYDRAULIC APPARATUS Frederick William Meredith, Cricklewood, London, England, assignor to S. Smith & Sons (Motor Accessories) Limited, Cricklcwood, London, England, aBrtishcompany Application October 19, 1942, Serial No. 462,567

In` Great Britain June 5, 1941 8 Claims n (Cl. 18S-96) This invention relates to hydraulic' apparatus of the kind comprising a pressure chamber `in which a hydraulic pressure may be obtained and a relatively movable part passing through a Wall of the chamber, a high-pressure seall being pro' vided between this part and the wall ofy the` chamber through which it passes. One example of this kind of apparatus is a piston and cylinder device operating as a pump or motor or a dashpot. In practice, there is usually some leakage of the liquid past the seal, and the chief object of the invention is to provide an apparatus in which this leakage is prevented.

According to the invention there isprovided a hydraulic apparatus of the kind specied comprising an outer chamber enclosing said .seal and encircling said relatively movable part so that any liquid leaking past the seal goes into the chamber and a header tank connected to this outer chamber and charged with the operating liquid so as to maintain said seal drowned. Thus, any liquid leaking past the seal merely passes into the outer chamber which is not sub@- jccted to pressure. closed around the relatively movable part by means of a simple soft 10W pressure packing. Furthermore, under conditions of low pressure in the pressure chamber liquid may leak past the high pressure seal in the reverse direction, to prevent cavitation or vaporization of the liquid, but preferably passages areprovided connecting the 'header tank or the outer chambers with the pressure chambers, these passages containing non-return valves permitting fluid to flow past the valves into the pressure chambers.

One application of the invention isto a piston and cylinder device in which the pistonrod extends on opposite sides of a piston Aout through high pressure vsealing means in opposite ends of the cylinder, andy according to a further feature of the invention an outer chamber encloses each sealing means and encircles the piston rod at each end of ,the cylinder which outer cham- ,bers both communicate with a space withinan outer cylinder which encircles the pressure The outer cylinder is thus charged with the uid at low pressure in addition to the outer chambers at its ends and only a single header tank is required communicating for instance with one of the outer chambers.' The pressure cylinder and the high pressure seals arev thus completely enclosed so as to prevent any leakage of liquid takinguplace...

The invention is more specifically concerned with `piston and cylinder'dashpot devices con- The outer chamber may be `taining a liquid which passes through bleed passages and a further feature of the invention consists in compensating for temperature effects. on the viscosity of the liquid' by the differential expansion of two different metal members for controlling one of said bleed `passages oneof which members is constitutedr by the piston rod.

The following is a description of one form of piston and cylinder dashpot device according to this invention, reference being made to the accompanying drawing, in which:

`ligurel is a longitudinal section through the device, and

Figure 2 is a section throughan alternative form of low pressure packing.

The piston I0 is liXed to a piston rod II extending from both ends of the cylinder I2' and the cylinder is closed 'by end caps I3 and I4 each formed with high pressure sealing bearing kI5 around the piston rod. Each end cap also houses a soft packing IB which is pressed by a gland nut I'l and a Washer I8 into a space between a retaining ring I9 and the piston rod. Between the high pressure sealing bearing and soft packing in each end cap there is an outer or low kpressure chamber 20 of annular form around c the pistonv rod and these chambers are connected by passages 2I formed in the end caps to an annularspace 22 Within an outer cylinder 23 enclosing the pressure chamber, the ends of this with liquid. The header tank is provided with a non-spilling cap 25. With lthis arrangement, no air` canbe drawn into the pressure cylinder 4but it must be expected that, due to changes of temperature and/,or pressure, dissolved air, will,

from vtime to time, be released from the liquid.

To enable this air to escape a small leak passage 26 is provided in the upper side of each end cap leading past thehigh pressure sealing bearing so Ias to permit such air to leak through the liquid in the header tank to atmosphere. Any air freed in the pressure cylinder at the side of the piston remote from the header tank will find its Wayrthrough the annularspace 22 to the passage 12| and thence to the header tank. In each of the end lcaps there is a passage 21 between the necting the two sides thereof, a metal piston rod extending on opposite sides of said piston out through said cylinder heads, which piston rodis hollow on at least one side of said piston, a rod located within the hollow piston rod on one side of the piston and extending into said bleed paspacking means between said rod and said cylin-v der heads. j l

8. A dashpot apparatus comprising ya pressure cylinder, a cylinder head at each "end thereof, a piston in said cylinder, ableedpassage extending` through said piston from one side to the other thereof, a metal piston rod extending on opposite sides of said piston out through said.- cylinder heads, which piston rod is hollow on at y least one side of said piston, a rod located within the hollow piston rod on one side of the piston and extending into said bleed passage, which rod is formed from a metal having a different coeicient of expansion than the metal of the hollow piston rod, and is fixed at the outer end to the piston rod, means for adjusting said rod axiallyI in relation to the piston rod, the other end of which rod is movable longitudinally within said bleedrpassage to control the :How of uid v therethrough, and packing means between said rod and said cylinder heads.

FREDERICK WILLIAM MEREDITH. 

